Monday, November 23, 2015
Solar Washington, Part Deux.
Our 2015 project involved assembling 400 square feet of solar atop a sturdy steel frame, once again courtesy of Boeing Surplus Sales. The clearspan structure was built from thirteen 20' sticks of SuperStrut steel channel, literally a big boy's erector set! There's no substitute to vastly overbuilt when it comes to amateur engineering, as each of those sticks could support 5000 lbs!
The modules came from electric vehicle co-conspirator Matt Moreno, who has limited area with solar exposure on his home, and decided to upgrade from these Kaneka 60 Watt thin film modules to the Iteks that dominate our Made in Washington market. These thin film modules are sometimes superior in our low light conditions, and the panel has complete coverage with active material between the frames, with no gaps as appear on mono or poly crystalline modules. Thin film can outproduce crystalline during diffuse, indirect or the low-angle sunlight that we often have here in the cloudy northwest. However, in terms of annual production per square foot, crystals are where its at. So, I got 32 of these at depreciated and friendly pricing, plus found six more new-old stock modules to square out the array and stock two spares from a depressed "Prepper" who never put them into use (which doesn't matter much because the world didn't end after all).
In order to not be too obtrusive on the neighbors and to maximize my covered storage space, (at the cost of 8% less annual production than optimal tilt of 34 degrees). I set this array at the minimum 6 degree angle required for drainage, and came up with a mounting method that made the roof rain-tight using continuous strips of aluminum to bridge the longitudinal gaps, and the steel channel frame catches rain from the horizontal gaps and channels it to either side. Like any simple shed, there is still dewfall below, but it is an improvement over sun and direct rain. Note that optimal tilt does not equal latitude here in the cloudy PNW. Most of our insolation comes during summer, so optimal tilt is biased towards summer production.
It was a nice bit of luck (that I pushed, of course) to get two arrays of the same rating; 2160 Watts from 36 Kanekas and 2160 Watts from the 8 Iteks! But wait, there's only one inverter, isn't there? Well, to maximize the state incentive scheme, I'm switching the Iteks over to Made in Washington Blue Frog microinverters, which apply maximum power point tracking to each single module in the array while producing grid-tied 240 VAC at the array. Normally this would be overkill on a dual-axis tracker, but my modules do see some shade in the early mornings and late afternoons, so this will squeeze a few more electrons out of it. This approach also fits into the theme of comparing technologies, and it will be interesting to watch the performance under different conditions and over different timeframes, as well testing as the long-term reliability of each. This will also allow reuse of both the AC and DC wires already passing under the lawn, without expensive rewiring.
Posted by Jay Donnaway